LA-ICP-MS zircon U-Pb ages of the A-type granites in the Lu-Zong (Lujiang-Zongyang) area and their geological significances

LA-ICP-MS zircon U-Pb dating for four A-type granites (alkalic intrusions) such as Chengshan, Huashan, Huangmeijian and Zongyang intrusions in the Lujiang-Zongyang area was carried out in this paper. These intrusions consist of monzonite and quartz syenite which contain a lot of K-feldspar. The whole-rock analytical results of major, trace and rare earth elements of the rocks indicate that they belong to a typical A-type granitoid association. LA-ICP-MS zircon U-Pb datings yield the ages of 126.5 ± 2.1 Ma, 126.2 ± 0.8Ma,125.4 ± 1.7Ma and 124.8 ± 2.2Ma for four intrusions, respectively. The results indicate that all A-type intrusions in the Lu-Zong basin formed in the Early Cretaceous from about 126Ma to 124Ma. These intrusions are characterized by relative high silica and alkalis, ascribed to metaluminous, has moderate REE and strong Eu depletion with a slightly right-inclined sea-gull REE pattern, all belonging to Al type granites. These data, together with other accuracy dating data of volcanic rocks and intermediate-acid high-K calc-alkalic plutons in the Middle and Lower Reaches of the Yangtze River area, support the occurrence of intensive lithosphere thinning at 126 Ma to 124 Ma, the peak period of crustal extension in the district.